In the laboratory analysis of specimens by any of the well-known analytical methods including infrared spectroscopy or chromatography, it is desirable to automatically submit a large number of samples or specimens to the instrument performing the analysis without constant attendance. A number of types of automatic sampling systems (referred to generally as "autosamplers") are known and have embodiments for both solids and liquids.
Discrete autosamplers have a large number of sample compartments in which the individual samples or specimens are placed. Flow is diverted from each compartment in sequence to the analysis instrument. In the case of solids and some liquids which must be analyzed in the form of vapor, the sample is pyrolyzed (rapidly heated in the absence of reacting gases) to cause vaporization of the solid or liquid.
Another type of autosampler is the carousel/stacked type wherein samples are placed in holders (for example, bottles) and the contents of the holders are sequentially transferred to a common sampling chamber. This system usually requires a heated transfer line. This type of autosampler is not suitable for solids.
Another form of autosampler is a robot system that can emulate the manual one-by-one sample transfer.
The discrete autosamplers have a number of drawbacks: namely, many expensive probes (sample holding compartments) are required; a large multi-position valve for selecting probes is required which may suffer alignment problems; calibration numbers are required for repeatability; a very high electromechanical input/output count is required to switch power and sense lines for control of the autosampler; the dead volume is large; manual loading directly to probes can cause damage to the pyrolysis coils; a heated column isolation load/unload chamber is required; and a large number of isothermal zones are required.
The carousel/stacked autosamplers also have drawbacks: namely, numerous mechanical movement commands are required to transport the sample to the sampling chamber; a large dead volume in the stand-alone unit; a heated column isolation load chamber is required; complicated means (magnetic, vacuum or tactile) are required to move the sample in and out of the sample chambers; a count of samples as loaded is required; the sample chamber must reside close to the carousel or within the range of the x-, y-, z-axes of a robot loader; a heated transfer line is required between the pyrolysis chamber and the gas chromatography inlet; and precision positioning is required.
U.S. Pat. No. 4,798,805 discloses an apparatus for pyrolysis and analysis, one sample at a time. U.S. Pat. No. 3,536,452 discloses a system in which reactor tubes are fixed in a carousel so as the carousel is rotated each tube may be connected to an input reactant line. U.S. Pat. No. 4,476,733 discloses an autosampler for a gas chromatograph wherein sample containers are covered with a pierceable cover. The containers are advanced to a heater and then the cover of the containers is pierced to capture the heated specimen.
It is an advantage, according to this invention, to provide an autosampler for a pyrolysis device that overcomes the disadvantages of the prior art.
It is a further advantage that with the autosampler disclosed herein, results are repeatable due to the use of a single heating coil, no exposure of the analysis column to air during loading and unloading, and carrier flow which may be maintained at all times. Also, there is little or no carryover between samples due to the removal of the tube or container in which pyrolysis previously took place and a purge and clean cycle between runs. Also, the sample is purged to vent after the sample is loaded in the sample chamber providing an inert atmosphere prior to pyrolysis.